Referring to FIGS. 1 through 5 of the drawings, there is illustrated a conventional pressure vessel of a boiling water reactor, which is an example of vessels to which the invention is applicable. In FIG. 1, the reactor pressure vessel, generally designated by the reference character A, comprises a body B and a lid C mounted on a top of the body B. The body B and the lid C have their respective end flanges D and E which are fastened to each other by means of a plurality of, e.g. 92, stud bolt and nut assemblies arranged in circumferentially equidistantly spaced relation on a pitch circle concentric to a center of the lid C. Each of the stud bolt and nut assemblies includes a stud bolt F having an axis thereof extending vertically and a nut G threadedly engaged with the stud bolt F. A plurality of sling fittings Ca are fixedly secured to an outer surface of the lid C at an intermediate height thereof, and project from the outer surface.
As clearly shown in FIG. 2, each of the stud bolts F has a threaded portion Fa formed at a lower end of the stud bolt F and a threaded portion Fb formed adjacent an upper end of the stud bolt F. The stud bolt F is formed at its upper and with a threaded grip portion Fc which is adapted to be gripped by a stud tensioner. The tensioner is for gripping the threaded grip portion Fc of the stud bolt F to pull up the same. The arrangement is such that the lower threaded portions Fa of the respective stud bolts F are threadedly engaged respectively with threaded bores in the flange D of the body B, the nuts G are threadedly engaged respectively with the upper threaded portions Fb of the respective stud bolts F, and the nuts G are tightened against the upper surface of the flange E of the lid C through washers H to thereby fix the lid C to the body B.
It is necessary for the reactor pressure vessel A to demount the lid C from the body B when fuel rods are replaced by new ones after initiation of the operation of the reactor, or when regular inspection is effected on the reactor. Demounting of the lid C from the body B is performed by the steps of the procedure illustrated in FIGS. 3 through 5.
At the outset, as shown in FIG. 3, the nuts G are successively loosened and released from threaded engagement with the respective upper threaded portions Fb of the stud bolts F, while pulling up the stud bolts F by the stud tensioner. In this connection, the sections of the respective upper threaded portions Fb exposed to the outside are beforehand cleaned by brushes or the like to prevent the nuts G from being seized to the upper threaded portions Fb. The nuts G and the washers H are then removed respectively from the stud bolts F. Subsequently, a crane, not shown, is employed to lift the lid C vertically along the stud bolts F and out of the latter, so that the lid C is demounted from the body B, as shown in FIG. 4. The demounted lid C is conveyed to a predetermined storage location.
Subsequently, as shown in FIG. 5, the stud bolts F projecting upwardly from the flange D of the body B are released from threaded engagement with the flange D and are detached therefrom. The detached stud bolts F are conveyed to a predetermined storage location in a manner like the lid C. Thus, all of the components are removed from the top of the body B, and then the fuel rod replacement operation or the inspection operation is effected.
Mounting of the lid C on the body B is performed by the steps of procedure reverse to the above-mentioned steps of procedure by which the lid C is demounted from the body B.
Locations of connection between the lid C and the body B by means of the stud bolts F are extremely numerous in number such as, for example, 92 in all about the lid C. Moreover, in general, each stud bolt F and each nut G are considerably large in size and heavy in weight, although they vary depending upon the size of the pressure vessel. For example, the stud bolt F having its length on the order of 1.8 meters becomes 250 Kg in weight. Furthermore, attaching and detaching operations of the stud bolts F and the nuts G are wholly effected within a controlled area. Thus, it is required to promote simplification and automatization of the operations in an attempt to shorten the working period and to reduce exposure of operators.
In order to meet the above requirements, the same assignee as that of the present invention has proposed some appropriate techniques in Japanese Utility Model Publication No. 58-17737 entitled "Attaching And Detaching Device For Stud Bolts" and in Japanese Patent Publication No. 59-11433 entitled "Nut Attaching And Detaching Operation Equipment". By such techniques, an attempt has been made at elimination or reduction of labor, shortening of the working period and reduction in exposure of operators, during the attaching and detaching operation of stud bolts and nuts.
Extremely difficult problems are encountered in the designing and manufacturing of a vessel lid mounting and demounting apparatus in which attaching and detaching of stud bolts and nuts are automatized. Specifically, as described previously, the stud bolt and nut assemblies used to connect the body B and the lid C of the reactor pressure vessel A to each other are very numerous in number, i.e., 92 in all about the single lid C. If an attempt is made to effect attaching and detaching of many of such stud bolts F and nuts G for a short period of time, it may be considered that a plurality of operating units each effecting automatic attaching and detaching of the stud bolts F and the nuts G are arranged and are operated simultaneously.
It is required for bolts and nuts employed in the reactor pressure vessel, however, to ensure higher reliability of tightening performance and the like. To this end, it is necessary to avoid problems such that the stud bolts F and the nuts G interfere with peripheral equipment or operating units during the attaching and detaching operation so that the threads on the stud bolts F and nuts G are damaged. It is also necessary that respective combinations of the stud bolts F and the nuts B before the lid C is demounted from the body B are maintained unchanged also after the lid C is demounted from the body B and is again mounted thereon, and that the removed stud bolts F and nuts G are used without failure at their respective initial locations, i.e., at the same locations as those before removal.
Accordingly, if a plurality of operating units are arranged as described above in an attempt to shorten the period of time required for the attaching and detaching operation of the stud bolts F and the nuts G, it is desired to correctly position the plurality of operating units at the stud bolts F and the nuts G, i.e., to vertically align the operating units with the stud bolts F and the nuts G, in order to prevent the operating units from inadvertently interfering with the threads on such stud bolts and nuts during the attaching and detaching operation thereof. Should an attempt be made to fulfill such desire, a mechanism for positioning the operating units would become complicated in structure, and would become extremely expensive. Otherwise, careful or fine adjustment in position would be necessary for each of the operating units, resulting in a prolongation of time required for the adjustment in position.